Generally, a reduction in loss of viscosity in the cap tread is often addressed by using a rubber that emphasizes rolling resistance and has a low tan δ at 60° C. in the cap rubber that configures the tread portion as a method for reducing rolling resistance of a tire. However, this type of tire leads to the problem of a reduced grip performance on wet road surfaces and recently there has been a strong demand for measures to improve wet grip performance.
Conversely, the preferable use of rubber emphasizing wet grip performance with a high tan δ at 0° C. as the cap rubber is known as a measure for improving wet grip performance of a tire. However, because there are limitations to obtaining a compound that has both a high tan δ at 0° C. and a low tan δ at 60° C. at the same time from a technical standpoint, the problem arises that it is extremely difficult to address the above demand by using a single compound as the cap rubber.
Conventionally, the disposition of rubbers having a plurality of types of different physical properties in the tire width direction of the cap rubber has been proposed in order to meet the required performance in a pneumatic tire (see for example, Japanese Unexamined Patent Application Publication Nos. H06-262907A and 2006-240507A). However, the measures for combining rolling resistance and wet grip performance are insufficient in either of the proposals and further improvements are required because of the disadvantage of uneven wear occurring easily due to the configuration of soft rubber in the center region in Japanese Unexamined Patent Application Publication No. H06-262907A, and the disadvantage of poor rolling resistance due to the disposition of a rubber emphasizing rolling resistance in a center portion and a rubber emphasizing wet grip performance in the shoulder portion in Japanese Unexamined Patent Application Publication No. 2006-240507A.